Conventional phase shift circuits used in a base-station antenna are described in Japanese Patent No. 4745213 (Patent Document 1) and U.S. Pat. No. 5,940,030 (Patent Document 2).
A phase shift circuit described in Patent Document 1 includes a signal line, a ground conductor provided to be opposed to the signal line, and a dielectric plate inserted between the signal line and the ground conductor from a direction perpendicular to a longitudinal direction of the signal line. In the phase shift circuit described in Patent Document 1, the overlapped area between the dielectric plate and the signal line is changed depending on the inserted length of the dielectric plate, and thereby controls the phase of the signal output from the signal line.
Patent Document 2 describes a phase shift circuit having substantially the same configuration as the phase shift circuit described in Patent Document 1. Nevertheless, the phase shift circuit described in Patent Document 2 has a characteristic impedance of a signal line changed by inserting a dielectric plate. That is, a circuit to match impedance is also incorporated to the phase shift circuit described in Patent Document 2.